Abstract: The cyclic plastical bebavior of GH33A supperalloy is investigated under the condition of simultaneous cycle of temperature and mechanical strain. Influance of phase difference of alternating temperature and mechanical strain(in-phase and out-of-phase) on cyclic softening or cyclic hardening and thermal mechanical fatigue life is studied. The experimental results show that the damage in in-phase thermal machanical fatigue is more serious than that in out-of-phase at 570~825℃.And, the material is serious cyclic softening at high temperature side and first cyclic hardening, then cyclic softening at low temperature side for both in-phase and out-of-phase in thermal mechanical fatigue.